A variety of amplifiers and oscillators exist for applications with operational frequencies below approximately 100 GHz. These include solid-state amplifiers and oscillators which are based on Gunn-effect diodes, impact avalanche transit time diodes, field effect transistors, and/or bipolar transistors. Other known approaches include vacuum sources such as klystrons, traveling wave tubes, and gyrotrons.
However, there are other types of systems in which there is a need for amplifiers and/or oscillators capable of operating at higher frequencies. For example, microwave systems need high-frequency amplifiers to improve the reception of signals, need high-frequency oscillators to serve as local oscillators in receiver circuits, and need high-frequency oscillators to serve as power oscillators in transmitter circuits. High-frequency amplifiers and oscillators for these applications have traditionally been implemented with large vacuum-tube devices, such as gyratrons, or with inefficient frequency-multiplied solid-state sources and parametric amplifiers. In this regard, frequency-multiplied solid-state sources translate an input signal at one frequency into a higher harmonic frequency, but at poor power conversion efficiency. Parametric amplifiers use driven, non-linear reactive elements to achieve power gain at high frequencies. While these existing approaches have been generally adequate for their intended purposes, they have not been satisfactory in all respects.